1. Field of the Invention
The present invention relates to a synthetic resin layered lens for a vehicle lighting device, which consists of a lower lens layer and an upper lens layer disposed on the lower lens layer, and a method of molding such a layered lens.
2. Description of the Related Art
FIGS. 8 and 9 show a typical conventional layered lens. As shown, the layered lens consists of two layers, a white lower lens layer 1 of lens and a red upper lens layer 3. The lower lens layer 1 has seal legs 2. The upper lens layer 3 is disposed on the lower lens layer 1, forming a layered lens of one piece construction. To manufacture the layered lens, a mold assembly as shown in FIG. 11 is used.
As shown, the mold assembly includes a fixed table 5 and a rotary table 6 located above the fixed table 5. The fixed table 5 includes molds A and B. The rotary table 6 includes molds C and D corresponding to the molds A and B. The lower lens layer 1 (indicated by a phantom line in FIG. 10) is first formed using the molds A and C. The rotary table 6 is then turned by 180.degree. in a state that the product (lower lens layer 1) is placed in the upper mold C. The upper lens layer 3 (indicated by a phantom line in FIG. 10) is formed on the lower lens layer 1, using the molds B and C. In this way, a one piece of the layered lens, consisting of the lower lens layer 1 and the upper lens layer 3 disposed on the lower lens layer 1, is manufactured. In the lens layer 1 and the upper lens layer 3 disposed on the lower lens layer 1, is manufactured. In the figure, reference numeral 7 designates an injection hole for injecting molten resin into the runner of the mold A. Numerals 8 and 9 designate nozzles for injecting molten resin into the injection holes 7.
The layered lens as the molded product has two gate scars G1 and G2 (see FIG. 9). The gate scar G1 is created in the seal legs 2 during the process for molding the lower lens layer 1. The gate scar G2 is created at the circumferential edge of the upper lens layer 3 during the process for molding the upper lens layer 3. These scars reduce the appearance of the lens. The scars also are dangerous to workers handling the lens. To avoid harm, an additional process to cut off the gate scars is essentially required.
The gate scar G1 creates another problem when the layered lens thus produced is assembled into a vehicle lighting device. When the seal legs 2 are inserted into the groove of the lamp body of the vehicle lighting device, air is introduced into the sealing material in the seal groove due to deformation caused by the gate scar. The air impairs the sealing material which seals the gap between the seal legs and the seal groove.
In the peripheral region of the gate scar of the layered lens, a stress region formed during the molding process remains as an initial stress. Gasoline, wax for car washing, and like, when applied, makes this stressed region fragile and more likely to crack. Cracks will lessen the water-proof characteristics of the lens.